Since ifhp calls ghostscript for this printer (-sDEVICE=cdj550), zoptions have to be gs-options!
For example, the command :
lpr -Pdj -Z-r60x60 file.ps
prints file file.ps with a very low resolution(60x60) and
lpr -Pdj -Z-bBitsPerPixel=1 file.ps
prints monocolour. For details on gs-options see the gs man-page or take a look at /usr/doc/gs/use.txt.gz.